diff --git a/app/models/compare.rb b/app/models/compare.rb
index 19ea2bc3065..feb4b89c781 100644
--- a/app/models/compare.rb
+++ b/app/models/compare.rb
@@ -41,21 +41,16 @@ class Compare
   end
   alias_method :commit, :head_commit
 
-  def base_commit
-    strong_memoize(:base_commit) do
-      return unless start_commit && head_commit
-      return OpenStruct.new(sha: @base_sha) if @base_sha
-
-      project.merge_base_commit(start_commit.id, head_commit.id)
-    end
-  end
-
   def start_commit_sha
     start_commit&.sha
   end
 
   def base_commit_sha
-    base_commit&.sha
+    strong_memoize(:base_commit) do
+      next unless start_commit && head_commit
+
+      @base_sha || project.merge_base_commit(start_commit.id, head_commit.id)&.sha
+    end
   end
 
   def head_commit_sha
diff --git a/spec/models/compare_spec.rb b/spec/models/compare_spec.rb
index 4200af0e0f5..8e88bb81162 100644
--- a/spec/models/compare_spec.rb
+++ b/spec/models/compare_spec.rb
@@ -37,28 +37,6 @@ describe Compare do
     end
   end
 
-  describe '#base_commit' do
-    let(:base_commit) { Commit.new(another_sample_commit, project) }
-
-    it 'returns project merge base commit' do
-      expect(project).to receive(:merge_base_commit).with(start_commit.id, head_commit.id).and_return(base_commit)
-
-      expect(subject.base_commit).to eq(base_commit)
-    end
-
-    it 'returns nil if there is no start_commit' do
-      expect(subject).to receive(:start_commit).and_return(nil)
-
-      expect(subject.base_commit).to eq(nil)
-    end
-
-    it 'returns nil if there is no head commit' do
-      expect(subject).to receive(:head_commit).and_return(nil)
-
-      expect(subject.base_commit).to eq(nil)
-    end
-  end
-
   describe '#base_commit_sha' do
     it 'returns @base_sha if it is present' do
       expect(project).not_to receive(:merge_base_commit)
@@ -87,13 +65,23 @@ describe Compare do
 
       3.times { subject.base_commit_sha }
     end
+
+    it 'returns nil if there is no start_commit' do
+      expect(subject).to receive(:start_commit).and_return(nil)
+
+      expect(subject.base_commit_sha).to eq(nil)
+    end
+
+    it 'returns nil if there is no head commit' do
+      expect(subject).to receive(:head_commit).and_return(nil)
+
+      expect(subject.base_commit_sha).to eq(nil)
+    end
   end
 
   describe '#diff_refs' do
-    it 'uses base_commit sha as base_sha' do
-      expect(subject).to receive(:base_commit).at_least(:once).and_call_original
-
-      expect(subject.diff_refs.base_sha).to eq(subject.base_commit.id)
+    it 'uses base_commit_sha sha as base_sha' do
+      expect(subject.diff_refs.base_sha).to eq(subject.base_commit_sha)
     end
 
     it 'uses start_commit sha as start_sha' do